This section provides background information related to the present disclosure which is not necessarily prior art.
Flue gas cleaning installations are extensively known in the prior art. An installation of the generic type is described, for instance, in WO 2006/032288 A1. By means of such installations, methods for the separation of harmful gases, for instance HCl, HF, SO2, are implemented. Also dioxins, furans and heavy metals, for instance mercury, can be effectively separated if additional so-called sorbents, such as hearth furnace coke, active carbon or the like are added. For the implementation of the method, fluidized bed reactors, into which the flue gas to be cleaned is fed in via a flue gas inlet unit, are customarily used. This unit is usually a pipeline led up from the boiler and having one or more outlets into the reactor region. In the reactor, a sorbent is stored or introduced. A fluidized bed is then formed in a known manner. Reactors can be operated with circulating fluidized beds or using an entrained-flow process. The flue gas and the sorbent react with each other and the harmful gases are in this way separated from the flue gas. The total gas, i.e. flue gas with the entrained separation residues and sorbent remnants, is relayed via a flue gas outlet unit into a downstream separation unit, usually filter units. In the filter unit, the flue gas is freed of the separation residues and subsequently released. The separation residues are in part fed back to the fluidized bed reactor or, after collection, disposed of or reused.
Thus it is in particular known from the prior art to use as the sorbent, for the desulpherization of flue gas, limestone (calcium carbonate; CaCO3) or slaked lime (calcium hydroxide; Ca(OH)2). As previously described, these are stored or introduced in the fluidized bed reactor. In recent years, the use of slaked lime has established itself as a more economical alternative to limestone, since the required quantity of slaked lime is about 1.8 times smaller compared to limestone. In addition, in the chemical reaction between flue gas and slaked lime, gypsum is produced, which can advantageously be reused.
Due to the high chemical reactivity of slaked lime, in particular the general handling, stockkeeping and introduction of this sorbent into the fluidized bed reactor has proved, however, comparatively complex. In the case of improper treatment, secondary reactions can hence occur already during storage or the feed to the reactor, which secondary reactions are accompanied by a depassivation of the sorbent and thus reduce the efficiency of the method. In addition, slaked lime has a comparatively strong corrosive effect compared to metals. As regards apparatus, this leads to increased wearing of the feed components of the cleaning installations, which adversely reduces the working life of these components and leads to increased maintenance and repair costs. Furthermore, slaked lime reacts strongly alkaline with moisture. In terms of the handling, comparatively high requirements have therefore to be placed on workplace safety, which is adversely associated with a further rise in process complexity and, in the event of accidents, can lead to a health risk for the persons involved.